Host-parasite coevolution and the Red Queen

Because parasites harm their hosts, natural selection favours host genes that make them resistant to parasites. Unfortunately, however, parasites are also under selection to overcome this resistance. Thus, hosts and parasites may co-evolve in continuous arms races of defence and counter-defence. Based on a character in Lewis Carrol’s Through The Looking-Glass (1871), such dynamics are often called “Red Queen” dynamics in evolutionary biology because hosts and parasites – like Alice and the Red Queen in the book – have to constantly be on the move without getting anywhere.

“Now, HERE, you see, it takes all the running YOU can do, to keep in the same place.” (Lewis Carroll, “Through the Looking Glass”)A very simple model of host-parasite co-evolution

Through mathematical models, we study how such Red Queen dynamics arise and how they are influenced by various factors. For example, we have recently shown that if environmental conditions alter the way that hosts and parasites interact genetically, then changing environments can both annihilate Red Queen dynamics that would otherwise occur, or generate Red Queen dynamics that would not occur in a constant environment (Mostowy & Engelstädter 2011). Other factors that we are interested in include properties of the infection genetics (Engelstädter & Bonhoeffer 2009), protective endosymbionts (Kwiatkoswki et al. 2012) and non-genetic inheritance (Mostowy et al. 2012).

It has also been suggested in the late 1970s that Red Queen dynamics can provide an answer to the longstanding and fundamental question of why most organisms reproduce sexually: through sex, co-evolving hosts may gain a advantage in the coevolutionary arms race. This “Red Queen Hypothesis” for the evolution of sex is now one of the major attempts to explain why sex and recombination are so common in eukaryotes but it remains poorly understood even at the theoretical level. Our work in this area aims at obtaining a complete picture of the conditions that favour or disfavour recombination under host-parasite coevolution. We have shown that recombination is indeed favoured with many different ways of how hosts and parasites interact genetically, but that recombination is also very often selected against (Engelstädter & Bonhoeffer 2009). In another project, we have shown that often, only the infected individuals in the population are selected to reproduce sexually, whereas sex is selected against within the healthy individuals (Mostowy & Engelstädter 2012).This is only a place holder.